Cycles texture mapping, generated coordinates with world orientation?
Yes, this is possible.
There are several ways to achieve this, here are a couple:
Position:
You can use the Position output of the Geometry node and separate out the blue (vertical) channel:

Note that since it's based on the world center some objects end up with values outside the 0-1 range:

Texture Coordinate:
You can also use the Object or the Generated output of the Texture coordinate node and convert it to world space with the Vector Transform node:

Now each object will have a gradient from 1 at the top to 0 at the bottom regardless of rotation: